1. Field of the Invention
This invention relates to filtering systems, more particularly filtering systems used in storm drains.
2. Prior Art
Stormwater flows into storm drains, often located on or near a street or highway, and into under ground lines. A problem associated with stormwater run-off is contamination with heavy metals and hydrocarbons which have leaked onto the streets and highways from a variety of sources. Sediment contained in the stormwater run-off also creates problems. Many times the contamination is so high that the storm water discharge exceeds the pollution limits imposed by federal and state laws. Thus, a need exists for a water-filtering device that can filter out heavy metal and hydrocarbon contaminants.
Prior attempts have been made to design filtering systems placed below the surface of the drain within the drain basins. For example, U.S. Pat. No. 4,419,232 to Arntyr et al. discloses a two-tier system whereby a coarse material filter is placed above a finer filtering material. Arntyr et al. discloses that the filter bag disclosed therein is capable of filtering out oil and other viscous impurities from the drain water, but only to a certain extent. As noted by Arntyr et al., the coarse filtering stage is necessary to prevent the filtering bag from breaking when filled with sticks rocks and other debris. U.S. Pat. Nos. 5,372,714 and 5,525,925 to Logue disclose the use of a subsurface filtering system whereby the filter is supported by a series of flaps which are sandwiched between the drain grating and a recess in the catch basin. The problems associated with this device are that the bag is susceptible to breaking for lack of support from below and that the flaps can become dislodged from between the basin recess and drain grating thereby causing the system to become inoperable. A further problem associated with the Logue device is the use of a woven polypropylene material. The woven material and lack of overflow outlets restrict the maximum flow rate through the system to about 40 gallons per minute per square foot and causes water flow to back up during heavy downpours, resulting in flooding around the drain. The use of a woven material also prevents the material from effectively filtering out the heavy metals and hydrocarbons. Thus, a need exists for a filter with increased flow capacity and the ability to filter out heavy metals and hydrocarbons.
The problems associated with the bag filtering systems in the prior art was disclosed ill U.S. Pat. No. 5,643,445 to Billias et al. As noted therein, the prior art filter systems using bags are constructed from material that is susceptible to breaking because of its short lifespan. Furthermore, the systems have no capability to allow storm water out of the system during period of heavy flow, causing flooding in surrounding areas. Applicants note that Arntyr et al. does in fact disclose flaps that open outwards for release of water during downpours. However, because these flaps open outwards, they can allow unfiltered water out of the system even when the filter is not full.
Throughout the United States there are many different sized storm drains, suggesting that a separate system for each size that may be encountered needs to be designed. However, this can become expensive and time consuming. There exists a need for a single storm drain filtering system that can be adaptable to all existing storm drains.